California requires that contractors add ground up waste tires to the asphalt mix on every road project. Blue Planet is now working with the state to pass legislation that would require highway contractors to use carbon recycled rock in their projects.
Photograph: Alamy

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But both public and private efforts haven’t stopped global temperatures from rising. Now, a growing number of scientists and innovators are arguing that we need to look at new ways to prevent more manmade CO2 from escaping into the atmosphere.

Brent Constantz, CEO of building materials company Blue Planet, says he has a good solution: sequestering waste carbon dioxide into manmade limestone.

BluePlanet, which was founded in 2006, collects carbon dioxide from California’s largest power plant, at Moss Landing, by bubbling the plant’s waste gases through seawater. The process removes about 90% of the carbon dioxide and combines it with minerals in the water, resulting in the creation of limestone that is composed of about 50% waste carbon dioxide.

Given that the Moss Landing plant produces more than 2m tons of carbon dioxide per year, this one plant could mitigate more than six times the carbon saved by Coca-Cola’s PlantBottle.

Cutting carbon out of cement production makes sense: cement manufacturing is responsible for an estimated 5% of global CO2. Adding to the problem, countries around the world mine and ship billions of tons of rock every year; in the US alone, 1.32bn metric tons of crushed rock were mined in 2015. If the carbon produced by those processes could be cut, it could result in a significant improvement.

A hotter world

This year, Earth hit a major milestone: for the first time in recorded history, September readings of atmospheric carbon dioxide, which are always the lowest of the year, didn’t drop below 400 parts per million.

James Hansen, the former head of the Goddard Institute for Space Studies and one of the world’s foremost climatologists, has argued that the reading needs to get below 350 parts per million, if, as he put it, we wish to “preserve a planet similar to that on which civilization developed and to which life on Earth is adapted”.

“It was a real crossing the Rubicon moment,” says Jamie Henn, co-founder of global warming activism group 350.org. “Nobody knows where the real tipping points are – the specific points at which global warming will become irreversible or will fundamentally change the Earth’s ability to support human life. But this September’s 400 parts per million moment is a real warning call that we’re crossing it.”

But some critics argue that this solution is untenable. Even beyond the common argument that it will weaken economic growth, there’s the fact that carbon taxes like the one levied in British Columbia, Canada have had a negligible effect in lowering CO2 emissions. Even carbon tax advocates are beginning to admit that it is only one of many carbon reduction policies that need to be implemented immediately.

Blue Planet has already begun branching out. It is currently working with cement manufacturers in Mexico and Canada, steel mills in Mexico, aluminum plants in Canada and coal-fired power plants in Wyoming to collect flue gases and use them to produce limestone. Constantz estimates that initially, each plant will produce between 50,000 and 100,000 tons of aggregate per year.

It’s not the only company working on finding ways to use waste CO2. Companies such as AirCarbon and Novomer use waste carbon to make plastic and textiles. Mineral Carbonation, an Australian company, is working on producing limestone from waste carbon, and Solidia, a US company, is also sequestering carbon in building materials.

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The policy side

Changes in government policy could make a huge difference when it comes to increasing the effectiveness of the carbon sequestration technologies being developed by Blue Planet, Mineral Carbonation and others.

Constantz cites California’s waste tire rubber initiative as an example of how policy can supercharge change. California requires that contractors add ground up waste tires to the asphalt mix on every road project. “It’s been 100% effective: there are no tires in California. We’re importing tires,” Constantz says.

In that vein Blue Planet is working with the state – as well as Ottawa, in Canada – to pass legislation that would require highway contractors to use carbon recycled rock in their projects. It helps that highway construction is already one of the biggest markets for cement and rock. Construction of a two-lane highway uses about 25,000 tons of crushed stone per mile, and almost 66% of that stone is limestone. “California uses 400m tons of rock every year,” says Constantz, noting that much of this material is paid for by the federal gasoline tax, which helps cover road upkeep. “We get $11bn dollars per year to buy rock and we import it from Canada and Mexico.”

If Blue Planet and its competitors can make artificial limestone at a competitive price, then they have the potential to become a major force for CO2 sequestration and reduction.

And this is a place where carbon taxes can help. Blue Planet receives a “royalty” of $10 for every ton of waste CO2 it collects in California, and Constantz estimates that, when Canada enacts its expected $30 carbon royalty fee and California raises its fee to $50 per ton, the economics of his limestone production will become even more attractive.

With a combination of price supports and market supports, countries have the potential to significantly advance carbon reduction.

Discussing the use of manmade limestone, Constantz is even more effusive: “That one move could solve climate change in the world,” he says.